Compressor control



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Jan. 1, 1952 A. B. NEWTON COMPRESSOR CONTROL 6 Sheets-Sheet 6 Filed Dec.17, 194'? Patented Jan. 1, 1952 UNITED STATES PATENT OFFICE COMPRESSORCONTROL Alwin B. Newton, Dayton, Ohio, assignor to Chrysler Corporation,Highland Park, Mich.,' a corporation of Delaware Application December17, 1947, Serial No. 792,277

Claims.

The present invention relates to the arts of refrigeration and airconditioning, the invention being applicable to a refrigerating systemof the compressor-condenser-evaporator type whether the system be usedto cool and dehu midify air for air conditioning purposes or to chill amedium surrounding the evaporator, such as air, salt brine, or a liquidsuch as diethylene glycol, which medium would be used for the purpose ofpreserving foodstuffs, producing ice, or any other purpose for whichrefrigerating systerns are of utility.

This application is a continuation in part of my application, Serial No.625,864, now abandoned.

The present invention is of particular application to a refrigeratingsystem including a compressor of the type disclosed and claimed in thepatent to Charles R. Neeson, No. 2,185,473, issued January 2, 1940, thepresent invention including a device responsive to a condition of airbeing conditioned or a condition of the medium surrounding theevaporator coil for effecting unloading and loading of the compressor ofthe refrigerating system in response to the condition.

The present invention involves a change in the construction of GonzalesPatent 2,304,999, December 14, 1942. According to that patent, a controlsystem has a part located in the medium being cooled so as to beresponsive to a given condition of the medium for acting on a valve rodfor a master valve operating a variable capacity means in a compressor.The valve rod is also connected to a means responsive to suetionpressure of the compressor such as a bellows. The arrangement is suchthat although the master valve for the variable capacity means isconnected both to the condition-responsive part in the medium beingcooled and to the suction-pressure-responsive means, theconditionresponsive part always has complete control of the mastervalve, and the suction-pressure-responsive means has control only in theevent that there is failure of control through the conditionresponsivepart.

According to the present invention, the control lies withthesuction-pressure-responsive means such as the bellows, and the partresponsive to a condition of the medium being cooled acts to modify thecontrol exerted by the suction-pressure-responsive means. The result isthat the suction pressure at which the compressor is unloaded is variedfor a variation of the aforesaid condition in the medium being cooled.

Also according to the present invention, means responsive to anadditional condition such as high suction pressure of the compressor mayact to unload the compressor, and this means may be coordinated with thecondition-responsive part to vary the control at the same point wherethe condition-responsive part varies the control. The advantage in a.control dependent upon high suction pressure is that it preventsoverloading of the compressor motor. If, for example, the refrigeratoris heavily loaded by a high temperature at the outset of the mediumbeing cooled, this is reflected in a high suction pressure. I havediscovered that the compressor should be unloaded for a reduction ofload on the motor if the heavy loading is to continue for a fairly longtime and that this may conveniently be done by unloading in response toa high suction pressure. The result is that the initial cooling periodmay be somewhat lengthened, but the compressor is not overloaded, andthe size of compressor may be determined from normal maximum load afterthe initial cooling period rather than from the overload that oftenoccurs in the initial cooling period.

The invention will be more fully understood by study of the followingspecification taken in connection with the accompanying drawings whereinlike numerals refer to like parts throughout.

In the drawings,

Fig. 1 discloses an air conditioning system having the present inventionapplied thereto, the compressor disclosed therein being of the typecovered by the aforesaid patent to Neeson.

Fig. 2 is a longitudinal section through a compressor having the presentinvention associated therewith, and showing details of the capacityvarying means disclosed in the aforesaid patent to Neeson;

Fig. 3 is a view in elevation of the front cover of the compressordisclosed in Fig. 2, with details of the capacity regulating mastervalve and the operating mechanism of the present invention attachedthereto;

Fig. 4 is an end view of the portion of the apparatus disclosed in Fig.3;

Fig. 5 is a sectional view taken through the master valve mechanism andthe operating mechanism;

Fig. 6 is a sectional view somewhat similar to Fig. 5, of a modifiedform of apparatus;

Fig. 7 is a plan view of the apparatus of Fig. 6;

Fig. 8 is a diagrammatic view of an electric circuit and associatedmeans for controlling the apparatus of Figs. 6 and 7; and

Fig. 9 is a sectional view similar to Fig. 6 of another modified form ofthe apparatus.

In Fig. 1 there is disclosed an air conditioning system comprising arefrigerating system of the compressor-condenser-evaporator type ofwhich I the compressor includes a pair of unitary compressors 20 ofidentical construction fastened to the opposite ends of a double-endedmotor 2|.'

The two compressors discharge in to a common condenser 22 from whichcondensed refrigerant is expanded into an evaporator 23 havingconnections to the inlets of both compressors. Therefore, for allpractical purposes the two compressing units may be considered as asingle compressor. The evaporator 23 is located in a duct 24 throughwhich a stream of air is drawn by a blower 25, the air passing over theevaporator being cooled and dehumidified and being then discharged intothe space to be served by the action of the blower. It is, of course,readily apparent that the evaporator may be located in a food storagecompartment over which air is circulated by a blower means or bygravity, or in a medium of liquid type used for various coolingpurposes.

Details of one of the compressing units are disclosed in Fig. 2 whereinit is seen that the compressing unit 20 comprises a crankshaft 30 towhich are connected a plurality of connecting rods 3| each operating apiston 32 in a cylinder 33. Gas which is admitted to the suctionmanifold 34 from the evaporator 23 passes into the interior of thecylinder through the suction valve 35 and is ejected through thedischarge valve 36 into the discharge head 3'! which is connected bypassage 38 to the common discharge manifold 39 from which the compressedgas passes into the condenser 22. Details of the valve and pistonconstruction may be ascertained from the aforesaid patent to Neeson, aswell as the patent to Charles R. Neeson, No. 2,137,965, issued November22, 1938.

As further explained in the aforesaid Patent No. 2,185,473, the suctionmanifold 34 is connected through ports 40 with the interior space 4| ofthe crankcase whereby a flexible, metallic bellows 42 is subjected tothe pressure of the expanded refrigerant returned from the evaporator.Movement of the bellows 42, which hasan end piece 42 soldered or weldedto a link rod 43, causes reciprocation of the linkrod 43 connected byrocking levers 44 to a master valve member 45. The master valve member45 (Fig. is provided with a plurality of notches 50 so that a springpressed ball 5| engaging in the notches permits step-by-step movement ofthe master valve member. Each step causes one of a plurality of slots 52to be connected to, or disconnected from, a source of oil pressurethrough an oil pressure tube 53. Each of the slots 52 is connected to ashort tube 54 leading to a cylinder 55 in which is mounted a springloaded unloader piston 56 connected to unloading mechanism including ayoke 51 adapted to ride on a ramp 58 and to be thereby moved axially asthe piston 55 moves the yoke 51 longitudinally. The yoke causes axialmovement of a ring 59 having unloader pins 60 mounted thereon, whichwhen moved axially outward cause the suction valve 35 to be held opencontinuously whereby the cylinder is unloaded or prevented fromcompressing refrigerant. The position of the variably movable valve part45, therefore, controls the number of unloader pistons 56 to which oilpressure is applied, and hence controls the number of cylinders inoperation. When, as disclosed in Fig. 5, all but one of the slots 52 areconnected to tube 53 through the annular space 5| surrounding thereduced portion of valve member 45, all but one of the individualcylinders will be loaded or operating. When valve member 45 is movedinwardly the length of another notch 50, two cylinders will be unloadedsince another one of the unloader cylinders 55 will be disconnected fromthe source of oil pressure. Oil pressure is applied to the unloadingmechanism through the master valve from a pressure lubrication pump (notshown), details of which may be ascertained from the aforesaid NeesonPatent No. 2,185,473. As disclosed in the aforesaid patent, the oilpressure pump operates coextensively with operation of motor 2| so thatno oil pressure will be supplied to the master valve 26 unless the motoris oper4 ating, and since it takes a short while for the pressure to bebuilt up by the oil pump it is apparent that all cylinders will beunloaded during starting, thereby preventing large starting currentinrush. It is also apparent that after oil pressure is available anumber of cylinders will be unloaded depending upon the position of thelinkrod 43.

The aforesaid Neeson Patent No. 2,185,473 discloses that the position oflinkrod 43 may be controlled by the degree of compression of theflexible, metallic bellows 42. which compression is efiected by thepressure of the gas in the space 4| connected to the suction side of therefrigerating system through the port 40. The pressure of the gasagainst bellows 42 operates against a compression spring 65 positionedbetween the end of the bellows and a disk 65. The disk has wings 66 atopposite sides projecting through slots in a threaded sleeve 61. Thesleeve is secured as by soldering or welding to an apertured member 68,to which the bellows 42 is secured. A nut 69 threaded on the sleeve 61determines the position of the disk 66 and consequently, the compressionof the spring 65. The link rod 43 has a reduced outer end on which isthreaded a nut 69* serving to guide the rod in the sleeve 61. A looknut-69 retains the nut 69 in position. In the aforesaid patent, it isexplained that the compression of the spring 65 controls the unloadingpressure of the master valve so that the suction pressure of therefrigerating system may be controlled within reasonable limits.However, it has been found in some instances that the pressure of thegas returning to the compressor is not quite an adequate measure of theconditions in the system that require unloading. Accordingly, I havedevised means for controlling the suction pressure at which unloadingoccurs and for controlling the position of the master valve part 45directly in response to one or more conditions of the medium beingcooled by the evaporator 23 such as temperature, humidity, or pressure.

As seen in Fig. 1, I provide an air pressure control system including anair compressor 10 operated by a motor 10 and discharging into a pressuretank 1|. The motor lll' is controlled by a pressure-responsive device lowhich causes the motor to operate when the pressure in the tank 1| fallsbelow a predetermined amount, the device 10* being connected in electricpower lines 10. Air is discharged from the tank through a pipe I l inwhich is located a pressure-reducing valve 11*, into a tank A pipe 12discharges compressed air from the tank H through pipes l2 and 12 intotwo pressure regulating valves 13 and 13. Valve 13 includes a pair offixed orifices 14 and 14 which maintain a steady discharge of compressedair at a constant pressure depending upon the pressure maintained intank II by the device 10 and the motor 10. The tank II has a safetyblowofi 15. The valve I3 has a space 16 into which orifice 'I4'discharges. The space 16 of valve 13 is connected to pipes 11 and I1which join in pipe 18, which branches into pipes 18- and 18 leading tohousings 19 and 80, respectively, each participating in the control ofone of the master valves 25. The pressure exerted in the housings 18'and 88 is controlled by regulating the pressure in pipe 11 which isaccomplished by valve 13 and by a second valve 13' interposed inparallel relation with valve I3 and connecting pipes 12 and I1. Valve l3includes a first chamber 18' operatively connected to pipe 12 and asecond chamber 16 operatively connected to pipe 11*. A partition whichseparates chambers 15' and 18 is provided with an orifice. A plunger 8|cooperates with this orifice to form a variable orifice valve meansadapted to vary the amount of air admitted to chamber 18 The plunger 8|is controlled by a diaphragm 82 and return spring 83. The position ofthe diaphragm 82 and plunger 8| are controlled by pressure in suctionline 85 leading from evaporator 23. This pressure is communicated by aline 85 to the diaphragm 82*. It is obvious that as the suction pressurein line 85 increases the diaphragm 82* and plunger 8| are forceddownward in Fig. 1 thereby increasing the amount of air admitted tochamber 75' and housings I9 and 80. The valve 13 includes a means forbleeding air to the atmosphere to load the compressor. This meanscomprises a plunger 8| operated by a bellows 82 and a return spring 83.The position of the plunger 8| is controlled by the pressure in a part84 connected to the space of which bellows 82 comprises a movable wall.Part 84 contains a fiuid reacting to a condition of the air or fluidmedium surrounding it, such as temperature, humidity, pressure etc. Astemperature rises, for example, bellows 82 is depressed and the pressurein space 18 drops as a result of increased opening of the valvecontrolled by plunger 8l. The orifices 14 and I4 provided in valve 13are required to provide a restriction so that when valve 13 is open apressure can be built up in pipe I8 even if the valve 13 is open. Whenvalve I3 closes after the compressor has been unloaded the pressure inhousings l9 and 88 is relieved through valve I3 when this latter valveis open.

As seen in Fig. 5, tube 18 is connected to a ring 85 forming part of thecasing 88. The rest of the casing is composed of a fitting 81 threadedon the ring 85, a seal 88 between the fitting and the ring, and a domemember 88 with a generally hemi-spherical end joined to the fitting asby soldering or-welding. The ring 86 has an inwardly extending fiange 80by which the casing 80 is attached to an end part 8| of the compressorwith the aid of screws 82. The screws also attach the apertured member68 to the end part 9|. The pressure of the air or gas in tube 18 istransmitted through the casing 88 and acts against the inner side of thebellows 42 so as to tend to expand it. The change of pressure exerted bythe air pump through the tube 18 by way of valve 13 acting in responseto change in condition of the medium being cooled and by way of valve I3acting in response to high suction pressure in line 85 is preferably soselected as to add or subtract from the efiect of spring 65 withoutrendering its effect negligible so that control of the master valve 45through the bellows 42 is retained by the suction pressure of thecompressor, the change in air pressure merely acting against the innerside of the bellows to modify.

the control of the master valve.

The operation of the present invention is as .follows: The compressorforces hot refrigerant gas into the condenser where the refrigerant isliquefied ,at the condensing pressure. The refrigerant is expanded inthe evaporator 23 and extracts heat from the air or other surroundingmedium. The expanded refrigerant is returned to the compressor andthrough the suction manitold 34 into the cylinders where it is againcompressed. The suction pressure, which refiects the load on theevaporator, exerts pressure on the bellows 42 which tends variably tocontrol the position of the unloader valve part 45. However, thiscontrol of the unloader valve part 45 is modified by the part 84responsive to a condition such as temperature, pressure, humidity, etc.,in the duct 24 and by a high suction pressure on the line 85, since theair or gas pressures in the housings 19 and 88 and the inner side ofbellows 42 are determined by the part 84 and the return line 85. As theair pressure varies, there is inward or outward movement of the valvepart 45 in steps controlled by the ball 5| riding in the notches 50. Themovement of the master valve part 45 controls the connecting ordisconnect-' lng of one or more of the unloader cylinder spaces 55 andthe source of fiuid pressure through tubes 53 and 54. When pressure isapplied to a cylinder space 55 the piston 58 therein is moved inward andcauses the yoke 51 to ride down on ramp 58, thus dropping the pins 88from the suction valve 35 and allo 'g the cylinder to compress gas.Disconnection of the cylinder space 55 from the source of fiuid pressurecauses the cylinder to become unloaded. In this manner the number ofcylinders in operation varies so that the capacity of the compressorvaries directly in response to the temperature produced by theevaporator.

The valve l3 acts to modify the control of the master valve 45 only whenthe suction pressure in the return line is very high. A high suctionpressure is due to a heavy load on the refrigerating system, which may,for example, occur when a food locker or building cooled by the systemis first being cooled. The load required to bring the temperature downto the desired value is many times heavier than that required tomaintain the desired value oftemperature. It is economically desirableto select a refrigerator system for the low rating required formaintenance of a certain temperature instead of one of a high ratingrequired for lowering to the certain temperature. Yet the system shouldnot be overloaded. According to my invention, I prevent such overloadingby making the compressor unloader responsive to a high suction pressure.This is accomplished by adjustment of the valve 13 which acts to adjustthe pressure exerted on the inside of the bellows 42.. When a certainhigh suction pressure is reached in the return line 85 such as wouldindicate overloading of the system, the plunger 8| changes the amount ofopening of the variable orifice valve in the valve 13. This change inopening is reflected in an increased pressure in the chamber 18*, whichis communicated to the interior of the bellows 42.

Figs. 6 and 7 show a modified form of apparatus in which the modifyingeffect of a condition such as temperature, pressure, or humidity in thecooling duct 24 and a high suction pressure in the return line 85 isapplied by electrical means to the valve rod 43. The reduced threadedend of the valve rod 43 is slidably guided in a sleeve 93 in which isthreaded an adjustable bolt 94 providing a limit to the movement of thevalve primary coil rod 43 to the left. The sleeve 93 is suitably mountedin a cage 96, which is threaded upon the sleeve 61. The cage 96 may beadjusted by rotation along the sleeve 61 and a jam nut 91 prevents suchrotation. A sleeve 98 is slidably mounted upon the sleeve 93 and withinthe threaded sleeve 01 and engages one end of a coil 'by means of a nutand bolt I03 to an arm I04 actuated by an electric motor I05, the armhaving its center of angular movement at I06. The motor I05 is bolted toa bracket I09 supported on the end part 9| of the compressor by screws92.

As seen in Fig. 8, the motor I05 is controlled by windings I08 and I09,one being adapted to rotate the motor in one direction, and the other,in the opposite direction. Associated with the windings I08 and I09 arecontact points IIO and I I I, spaced as shown above and below a movableswitch member II2 pivoted at H3. The switch member has legs H4 and H5,which extend respectively through coils H5 and H1. The coil I I6 isconnected in a line I I9 at one end of which is connected a resistanceH9 and at the other of which is connected a resistance I20. The coil II1 is connected in a, line I2 I, at one end of which is connected theresistance I20 and at the other a movable arm I22 controlled by apressure-responsive element I23. The arm I22 contacts a resistance I24connected by a line I25 to the resistance H9. The resistance H9 iscontacted by a movable arm I26 controlled by an element I21 responsiveto a condition such as temperature, pressure, or humidity, the elementbeing conventionally represented as a bellows. The arm I26 is connectedin a line I28, connected to a secondary coil I29 of a transformer havinga I30. High voltage is impressed across the primary coil I30, and a lowvoltage is taken from the secondary coil I29. A line I3I leads from ajunction point I32 with the line I28 to the motor windings I08 and I09,which are shown to be connected in parallel with one another. The motorI05 controls an arm I33 connected by a link with an arm I35 contactingthe coil I20 and connected by a line I36 with the secondary coil I29.The switch member II2 is connected to the line I36.

When, as viewed in Fig. 8, the portions of the resistances H9 and I20 tothe left of the arms I26 and I35 equal the effective portion ofresistance I24 and the portions of the resistances H9 and I20 to theright of the arms I26 and I35, the secondary current is divided equallybetween line III! and lines I2I and I25. Thus the same pull is exertedby the coils II6 and H1 upon the legs H4 and H5 of the switch II2 andthe left end of the switch is maintained as shown in Fig. 8, out ofcontact with the points H and III. However, if more current flowsthrough the coil II1 than through the coil II6, a greater pull will beexerted upon the leg II than upon the leg H4, and the left end of theswitch moves up into contact with point IIO, causing current to fiow inthe coil I08. This makes the motor I05 rotate in a clockwise directionas viewed in Fig. 8. If a greater current flows in the coil IIB, theswitch I I2 contacts the point I I I, causing current flow in the coilI09 and rotation of the motor I05 in a clockwise direction in Fig. 8.Rotation of the motor causes angular movement of the arm I04 andmovement of the sleeve 98 to the left or right. The sleeve 98 actsthrough the spring 99 against the plate 42 of the bellows 42'. Thisadjusts the valve rod 43 and changes the suction pressure at which thecompressor unloads.

Any change from the position of equilibrium of Fig. 8 in which theswitch II2 causes no current to flow either in the coil I08 or in thecoil I09 is brought about by a change in position of the arm I25 or thearm I22 due to a change in the condition to which the element I21 or I23is respon sive. Let it be assumed that the element I21 corresponds tothe part 84 and valve 13 of Fig. l, or in other words, that the elementI21 is responsive to a condition of the medium being cooled in the duct24, such as temperature, humidity, or pressure. Assume that thecondition in question is temperature and that the element I21 willexpand with increase in temperature and contrast with decrease intemperature. Assume further that there is an increase in temperature.The resultant expansion of the element I21 will shift the arm I26 in acounterclockwise direction, causing less of the resistance II9 to be tothe left of the arm I25 and more of the resistance to be to the right.This causes a greater current to flow in the coil II6 than in the coilH1 and the switch II2 moves down to the point III causing current toflow in the coil I09. This causes the motor I05 to rotate in acounterclockwise direction as viewed in Fig. 8. The arms I33 and I35 areshifted counterclockwise, and the portion of the resistance I20 to theright of arm I35 decreases, and the portion to the left increases. Thuscompensation is provided for the decrease in the portion of resistanceII9 to the left of arm I26 due to counterclockwise shifting of arm I26,and when the portions of the resistances I I9 and I20 to the left of thearms I26 and, I35 again equals the effective portion of resistance I24and the portions of resistances H9 and I20 to the right of arms I26 andI 35, the current becomes the same in both coils II6 and H1, causing theswitch II2 to move out of contact with point III to the position of Fig.8. Current no longer flows in the coil I09 and rotation of the motor I05and shifting of the arms I33 and I35 stop.

The above described counterclockwise rotation of the motor I05 as viewedin Fig. 8, due for example to an increase in temperature in the duct 24causes the arm I04 to shift clockwise as viewed in Fig. 6. This shiftsthe sleeve 99 to the left reducing the force applied through the spring99 to the plate 42. The bellows 42 is thus permitted to collapsesomewhat, moving the valve rod 43 to the left and causing an increase inthe amount of loading of the compressor.

From the above it can readily be pictured what a reduction in thetemperature of the medium being cooled in the duct 24 will do to theapparatus of Figs. 6 and '1.

Consider that the element I23 corresponds in function to the valve 13and is subject to a suction pressure in the return line so as to act inresponse to a high suction pressure indicative of overloading of thesystem. Assume that the element I23 is so connected with the return line85 that this undesirable high suction pressure will collapse the elementI23 to the point where the arm I22 reduces the effective portion of theresistance I24. This increases the current in coil II1, causing switchII2 to move up into contact with point II 0. Current now flows in coilI08, causing clockwise rotation of motor I05 as viewed 9 in Fig. 8. Thiscauses clockwise shifting of arms I33 and I35 and an increase in theportion of the resistance to the right of arm I35. When the arm I35 hasshifted sufliciently in a clockwise direction, the various resistancesare so balanced as to cause the same flow of current in coils H6 and H1,and the switch II2 returns to the neutral position of Fig. 8, and themotor I05 is stopped. In the meantime, the arm I04 has shifted in acounterclockwise direction, moving the sleeve 98 to the right andcausing it to act through the spring 99 to urge the plate 42 of thebellows 42 to the right. This moves the valve rod 43 to the right andthereby increases the amount of the unloading of the compressor.

The apparatus of Figs. 6 and 7 provides for modification of the controlof unloading of a compressor determined by suction pressure throughelectrical means that are responsive to two different conditionsoccurring simultaneously, for example, a condition of a medium beingcooled such as temperature, pressure, or humidity and another conditionsuch as high suction pressure in the return line of the compressor.

The apparatus of Fig. 9 is also electrically controlled in the mannerillustrated in Fig. 8, but differs from that of Figs. 6 and 7 in certainrespects. A disk I31 engages the left end of the valve rod 43. One endof a coil spring I38 engages the disk I31, and the other end is engagedby a sleeve I39. The sleeve and spring are mounted within the threadedsleeve 31. The sleeve is pivotally connected to and between the spacedends of strips IOI forming the link I02, which is pivotally connected bynut and bolt I03 to the arm I04, actuated by the electric motor I05. Themotor may be controlled by a means like that of Fig. 8. The motor mayact through rotation in a certain direction to produce acounterclockwise shifting of arm I04, which brings about movement to theright of sleeve I39. The sleeve urges the spring I38 against the diskI31, causing the valve rod 43 and bellows disk 42 to be urged to theright. This action increases the unloading of the compressor.

Rotation of the motor I05 in the opposite direction causes clockwiseshifting of arm I04 and movement to the left by link I0! and the sleeveI39. The compression of the spring I30 is decreased, and the valve rod43 moves to the left under the action of the bellows 42. The unloadingof the compressor is thus decreased. The compression spring 65 actingbetween the bellows disk 42 and the disk 60 positioned by the nut 69threaded on the sleeve 61 resists collapse of the bellows 42 by thecompressor suction pressure.

I claim:

1. Unloading mechanism for a variable capacity compressor adapted to beconnected to a cooling system and having a plurality of compressingcylinders, each of a number of which may be selectively renderedinoperative in order to vary the capacity of the compressor, comprisinga plurality of individual cylinder unloading means each operativelyassociated with a single cylinder, fluid pressure creating means foroperating said individual cylinder unloading means, means forselectively connecting said fluid pressure creating means to saidindividual cylinder unloading means comprising a master valve includinga valve rod adapted to be selectively positioned at a plurality ofpositions, and means for selecting the position of said valve rodcomprising a spring biased to move said valve rod in a first direction,a bellows subjected on one side to the suction pressure of saidcompressor and operating against said spring for returning said valverod in the opposite direction to a plurality of successive positionswhen the suction pressure rises successively above a number ofpredetermined pressures, means for supplying pressure fluid against theother side of the collapsible bellows as to tend to expand the same formoving said valve rod in said first direction against the force exertedon the bellows by the aforesaid suction pressure, and means forcontrolling the extent of movement of said valve rod caused by theaction of pressure fluid against the said other side of the bellows,said controlling means comprising a device for regulating the pressureexerted by the pressure fluid and means responsive to the temperature ofthe medium subjected to the action of the cooling system and responsiveto the suction pressure of the compressor for variably controlling thesetting of the device.

2. Unloading mechanism for a variable capacity compressor adapted to beconnected to a cooling system and having a plurality of compressingcylinders, each of a number of which may be selectively renderedinoperative in order to vary the capacity of the compressor, comprisinga plurality of individual cylinder unloading means each operativelyassociated with a single cylinder, fluid pressure creating means foroperating said individual cylinder unloading means, means forselectively connecting said fluid pressure creating means to saidindividual cylinder unloading means comprising a master valve includinga valve rod adapted to move in a first direction to effect the fluidconnection and cylinder loading and to move in a second direction tointerrupt the fluid connections and unload the compressor cylinders andto be selectively positioned at a plurality of positions each of whichcorrespond to the loading of a selected number of said cylinders, andmeans for selecting the position of said valve rod comprising a bellowsoperatively connected to said valve rod, means for supplying pressurefluid against one side of the bellows so as to tend to move said valverod in said second direction to unload compressor cylinders, and meansfor controlling the extent of movement of said valve rod caused by theaction of the pressure fluid on said bellows comprising a device .forregulating the pressure exerted by the pressure fluid and meansresponsive to high compressor suction pressure and low temperature ofthe medium subjected to the action of the cooling system for providingincreased fluid pressures to move said valve rod in said seconddirection to eiTect unloading of said compressor cylinders.

3. A cooling system comprising a compressorcondenser-evaporator systemof refrigeration, the compressor of which comprises a plurality ofcylinders and means to vary the number of cylinders compressingrefrigerant comprising individual cylinder unloading means associatedwith each of a number of said cylinders, fluid pressure means foroperating said individual cylinder unloading means including a mastervalve having a valve rod capable of being moved to a number of controlpositions to vary the number of said individual cylinder unloading meansoperatively connected to said fluid pressure means, and means forselecting the control position of the rod, said means comprising anexpansiblecollapsible device subjected at one side to the suctionpressure of the compressor, means for subjecting the other side of theexpansible-collapsible device to pressure fluid, and control meansoperative to regulate the pressure of said last mentioned fluid inresponse to variations in both compressor suction pressure andevaporator temperature.

4. In a refrigerating system of the compressorcondenser evaporator type,capacity varying means associated with the compressor for altering theamount of refrigerant compressed, said capacity-varying means includinga master valve capable of being moved to a number of control positions,an expansible-collapsible device conn cted with the master valve andsubjected over a' flrst pressure area to the suction pressure of thecompressor to move the master valve, means for supplying pressure fluidto oppose said suction pressure on a second and substantially equalpressure area associated with said master valve, and means responsive tothe temperature of the medium being cooled by the evaporator of thesystem and to compressor suction pressure for varying the pressure ofthe pressure fluid.

5. In a refrigerating system of the compressor-condenser-evapora'tortype, capacity-varying means associated with the compressor for alteringthe amount of refrigerant compressed, means responsive to increasedsuction pressure of the compressor for exerting control over thecapacity-varying means tending to increase the compressor capacity,means responsive to a high temperature of the medium being cooled by thesystem for adjusting the control in a direction tending to. increase thecompressor capacity and means responsive to compressor suction pressuresabove a predetermined value tending to decrease the compressor capacity.

6. Inc. refrigerating system of the compressor-condenser-evaporatortype, capacity-varying means associated with the compressor for alteringthe amount of refrigerant compressed, means responsive to suctionpressure of the compressor for exerting control over thecapacity-varying means, means responsive to the temperature of themedium being cooled by the system for ad- Justing the control exerted bythe means responsive to suction pressure, and means responsive to a highsuction pressure indicating overloading of the compressor for modifyingthe control exerted by the capacity-varying means in such a way as toreduce the amount of refrigerant compressed.

'7. In a refrigerating system of the compressor-condenser-evaporatortype, capacity-varying means associated with the compressor for alteringthe amount of refrigerant compressed, a pressure-movable deviceassociated with the capacityvarying means so as to cause the same todecrease the amount of refrigerant compressed when subjected to pressurefrom one direction, means response to a low temperature of the mediumbeing cooled by the system for applying pressure in the said onedirection over a, predetermined area to the pressure-movable device andmeans responsive to an overloaded compressor condition for applyingpressure in the said one direction over an equal area to thepressure-movable device.

8. In a refrigerating system of the compressor-condenser-evaporatortype, capacity-varying means associated with the compressor for alteringthe amount of refrigerant compressed, an expansible-collapsible devicesubjected on its outer side to suction pressure of the compressor andassociated with the capacity-varying means so as to cause controlthereover to be exerted by suction pressure, a first spring engaging theinner side of the expansible-collapsible device, means 12 engaging thefirst spring for causing it to exert a predetermined force against theexpansiblecollapsible device, a second spring acting against theexpansible-collapsible device, and means re- I sponsive to thetemperature of the medium being cooled by the system and a high suctionpressure indicative of overloading of the compressor engaging the secondspring for causing it to exert a variable force against theexpansible-collapsible device in opposition to the force exerted on thedevice by the suction pressure for modifying the control exerted by thesuction pressure.

9. In a refrigerating system of the compressor-condenser-evaporatortype, capacity-varying means associated with the compressor for altering the amount of refrigerant compressed, an expansible-collapsibledevice subjected on its outer side to suction pressure of thecompressor, a rod extending through and fixed to an end of theexpansible-collapsible device, means associating the end of the rodoutward of the expansib1e collapsible device with the capacity-varyingmeans for causing the suction pressure to act through the device andtherod for exerting control over the capacity-varying means, a firstspring engaging the inner side of the said end of the device, meansengaging the first spring for causing it to exert a predetermined forceagainst the device in opposition to the force exerted thereon by thesuction ressure, a second spring acting against the ot r end of the rod,and means responsive to the temperature of the medium being cooled bythe system and a high suction pressure indicative of overloading of thecompressor for acting against the second spring to cause it to act witha variable force through the rod against the device in opposition to theforce of the suction pressure acting thereagainst for modifying thecontrol exerted on the capacity-varying means by the suction pressure.

10. In a refrigerating system of the compressor-condenser-evaporatortype, capacity-varying means associated with the compressor for alteringthe amount of refrigerant compressed, means responsive to suctionpressure for exerting a control over the capacity-varying means, anelectric motor for modifying the control exerted by the means responsiveto suction pressure over the capacity-varying means, parallel linesconnected with a power source and having resistance, means responsive todisturbance of a predetermined relation of the resistances in theparallel lines for operating the motor, means responsive to thetemperature of the medium being cooled by the systern for varying therelation of the resistances in the parallel lines, means responsive tohigh suction pressures indicative of overloading of the compressor forvarying the relation of the resistances in the parallel lines, and meansdriven by the motor for restoring the predetermined relation of theresistances in the parallel lines to stop the motor.

ALWIN B. NEWTON.

(1o REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number

